[tortugaranger]

The V4 board with installed LDR module with most of the components annotated

[tortugaranger]

Still have a ways to go yet but the V4 hardware manual has just been substantially updated to reflect the final prototype.
The V4's manual is now fairly verbose and goes into more detail on the basis of design and fundamentals than earlier versions.

Here's the link to the ePot.V4 hardware manual:  https://tortugaaudio.com/docs/epotv4-max-hardware-manual/

[tortugaranger]

Here are several photos of the V4 board with the Solid State Preamp Buffer module. The first photo is the buffer module by itself without the LDR module installed. All the rest show the buffer module installed on the V4 board with the LDR module included.

The buffer module is entirely optional but will convert the passive V4 into an active preamp volume/controller with adjustable gain from unity to +12 dB using plug-in gain modules. I'm still tweaking the buffer module design so it's likely the V4 will be released first with the buffer module to be released some time later.

[tortugaranger]

The Tortuga Audio website has a new home page and is all about the new and soon to be released ePot.V4 LDR stepped attenuator & preamp controller. Check it out!

https://tortugaaudio.com/

[tortugaranger]

Hi All,

Early Nov development update.

Overall things are finally coming together on the V4 development front and we are on track for releasing the V4 before year's end. But there's always something. I noticed that when I upped the gain to 12 dB on the buffer module, that there was a noticeable low level hum coming from the speakers. That started a search for the cause. After challenging every aspect of the buffer board design, and the V4 board itself, the ultimate cause of the noise was the OLED display. Essentially the same OLED display I've been using for several years now. Turns out the hum was always there but it wasn't until the buffer board amplified it that it became an audible issue. I'm actually a bit perplexed that I hadn't noticed this sooner.

So I took a deep dive into the OLED display itself and discovered that the OEM controller for the display, which runs off of 3.3 volts from the V4 board, has its own dc-dc switching boost converter that generates 12 volts used internally to refresh the OLED display screen. This converter is the cause of the 100-200 hertz noise. Turn off the OLED display and the noise goes away completely because this converter turns off as well. After evaluating corrective options, I'm going to add an isolated power converter to our OLED interface board. The isolated power converter converts 3.3 volts into 3.3 volts with its own independent ground separate from the V4 itself. This will prevent any OLED noise from traveling upstream into the V4 controller and the buffer board (if one is present).

This will require one more iteration on the OLED adapter board design which will likely take until mid-November before I have updated hardware on hand and am able to  test out the fix.

Aside from this issue, the V4 board design is done and I have production blanks on hand already. I may tweak the buffer board and linear power supply board designs slightly and order updated blanks on those too while we wait on the OLED adapter updates.

Almost there,
Morten

[tortugaranger]

Hi All,

Mid'ish November development update.

I had been chasing a source of low frequency hum in the 100-200 Hz range which I'd traced to the OLED display as a source. However, I also determined that this noise only manifested when I had the optional active buffer board plugged into the V4 board. No such hum is present when using the V4 board alone as a passive attenuator. After numerous attempts to isolate and eliminate the active buffer hum, I finally arrived at a fix by isolating the split +/- 12 volt power and ground used by the buffer. Isolating the buffer ground from the power that runs the V4 board and the OLED board did the trick. No more sneaky ground loops. This fix is easily accomplished through the use of isolating switching DC-DC regulators.

That got me thinking about the linear power supply and after some last minute testing and research I made the decision to change the optional stand alone power supply board from a classically linear design to a hybrid switching-linear design. The hybrid PS can be powered either from 90-250 VAC 50/60Hz mains or your own external source of 5 volt DC power. AC mains power produces raw 5 VDC via a switching AC-DC converter. Regardless of the source, the raw 5 VDC drives 2 different isolated DC-DC boost converters with one producing split rail +15/-15 volt DC power and the other producing a single rail of +9 volt DC. All of these DC voltages are on an isolated ground. All three switching voltages are then run through separate second stage linear regulators resulting in clean low noise +12/-12 and 5 volt regulated DC power. The result is the best of both worlds with effectively zero low frequency ripple with no hum, and with most of the higher (above audible) frequency switching noise significantly suppressed by the linear regulators and bypass caps. An added benefit of the hybrid approach is significantly reduced weight and size. 

Meanwhile I've started production of the main V4 boards and expect to begin shipping V4 product by early December. Finally! 
To clarify, only the V4 Max board, the OLED display, and the optional V4 buffer board will start shipping initially. A Mini version of the V4 will come later in 1Q25. The new hybrid PS board will lag the V4 by a few weeks since I'm still finalizing changes to its design per the above.

Cheers,
Morten

[Hikmer]

Are you ready to begin taking orders for an upgrade to my LDR3000x.V3 at this time?  I've been having issues with it intermittently shutting down and as of right now its just collecting dust so can ship to you at your convenience. 

[tortugaranger]

Are you ready to begin taking orders for an upgrade to my LDR3000x.V3 at this time?  I've been having issues with it intermittently shutting down and as of right now its just collecting dust so can ship to you at your convenience.

The short answer is yes eventually but not yet. Most 3000 series preamps are balanced. However, the left channel V4 board is a special expansion board rather another full V4 board. I have yet to finalize and finish testing of the V4 expansion board but that will get done in 1Q25. For those with single-ended Tortuga preamps, I will start taking orders for upgrading any of those to V4 soon after release of the V4 and getting the backlog of pre-orders out the door.

[tortugaranger]

Hi All,

Quick update for anyone interested in reading more about the new V4 preamp controller. I've just finished editing both the hardware and operating manuals for the V4.

You can find them via the links below.

Operations & Control Manual here: https://tortugaaudio.com/docs/epot-v4-operation-control-manual/
Hardware Manual here: https://tortugaaudio.com/docs/epotv4-max-hardware-manual/

[tortugaranger]

I am pleased to announce that the V4 LDR attenuator & preamp controller is now available and shipping has begun on our backlog of pre-orders.
Here's the link to the V4 product page:  https://tortugaaudio.com/products/diy-preamp-components/epotpi-v4-max-electronic-stepped-attenuator/

The V4 itself, the optional new solid state buffer board, the updated OLED display, and the new Function remote, are all available for order now.

The optional power supply for the buffer board plus the V4 expansion board for balanced audio applications will both be available early next year.

Cheers,
Morten

Photo of the V4 board with the optional buffer board installed.

[tortugaranger]

Now that the V4 Max board has been released, I'm now close to finalizing the layout of the smaller V4 Mini.

THE big difference between the V3 vs. V4 Mini is that the V4 Mini retains full LDR calibration capabilities - same as the Max.

The key differences between the V4 Max and Mini are:

1) Mini is only a single input device (no input switching)
2) Mini is for single-ended audio only  (no balanced audio)
3) Mini has built-in encoder - can be panel mounted same as a volume pot
4) Mini is 50% physically smaller (board area) than the Max

[DARTH AUDIO]

Morten, check your email and voicemail. I’ve left you messages with no response.

[tortugaranger]

Morten, check your email and voicemail. I’ve left you messages with no response.

Apologies for letting this fall between the cracks. Check your PM later today.

Regards,
Morten

[tortugaranger]

Now that I'm almost caught up with V4 pre-orders and a handful of V4 upgrade projects with older version preamps, I was able to finally launch the V4 firmware updating manual in the V4 online documents. While I've tested this method and verified it works on my end, it remains untested by customers. I will be getting customer feedback next week from at least one person who I know will be trying this.

V4 firmware update manual:  https://tortugaaudio.com/docs/epot-v4-firmware-updating/

With any new model, there's always an initial flurry of mostly minor firmware updates/fixes over the first few weeks of release. The V4 has been no exception. So far, there's only one significant change in the firmware that warrants all early adopters update their V4 boards to firmware version 1.0.6 or later. Rev 1.0.6. adds watchdog timer safety feature that forces the controller to reset itself safely should the processor every freeze or encounter a fault. That feature was unfortunately left out of earlier versions.

I'm pleased that initial customer feedback on sonic performance has been all super positive. While I'm certainly biased, there's no doubt in my mind that the V4 is THE most satisfying LDR based attenuator/controller to listen to that I've ever designed/sold.

Regards,Morten

[Hikmer]

So I just got back my LDR3000x Active Tube upgraded to V4 and I have to say it sounds fantastic.  Great work Morten!  By the way, I swapped out the tubes with a pair of Amprex 7308s and am quite blown away.  I know they are pricey and rare, so I will only use them on special occasions.    I also have a pair of PHILIPS PCC88 (7DJ8) but unsure those are compatible with your preamp as your page doesn't reference them.  Hoping I can get an answer on this, thanks!

[familytree2000]

Hi Hikmer.   Morten if your reading this.  Are you able to upgrade the LDR3000t with the new boards? 

[tortugaranger]

So I just got back my LDR3000x Active Tube upgraded to V4 and I have to say it sounds fantastic.  Great work Morten!  By the way, I swapped out the tubes with a pair of Amprex 7308s and am quite blown away.  I know they are pricey and rare, so I will only use them on special occasions.    I also have a pair of PHILIPS PCC88 (7DJ8) but unsure those are compatible with your preamp as your page doesn't reference them.  Hoping I can get an answer on this, thanks!

Hi. Sorry for the slow response. Just got back from 2 weeks in Scandinavia and am still in the process of adjusting. I do not care for those 12 hour flights and the 9 time zones.

Glad you're liking the V4 upgrade. Your LDR3000x was one of only a few that got built right before I stood down from building new preamps. As part up the V4 upgrade I did a redesign of the power supply board which I was never quite happy with earlier. I also had to do a minor update to the tube buffer board to fit with the V4 controller but made no basic design changes to the tube buffer circuitry. The combination sounded really sweet on my end. I was very pleased with the results.

Pretty much any of the 9 pin 7DJ8/6DJ8 family tubes will work including 6922, 7308 etc.  I believe the 7DJ8 run a 7 volt heater rather than the more typical 6.3 volts which the LDR3000x uses for the 6H30P and most other such 9 pin tubes. Heater current is often a key limiting factor in swapping various 9 pin tubes around but since the 6H30's use a higher current than all those other tubes, the LDR3000x will run on them. Now whether they sound better or not than the 6H30 is open for debate since the tube circuit used in the LDR3000x runs at a very odd 30V "slack" plate voltage instead of the typical 300-600 volt range typical of most tubes. That this works at all is due to the linearity of the 6H30's at very low plate voltages and where the gain of the tube circuit is minimal. After all, the tube circuit in the LDR3000x is a 2 stage buffer with little to no gain so gobs of plate voltage simply aren't needed. You'll get pushback from tube people on this point but you've listened to it and it definitely does not suck! Not all otherwise compatible tubes will perform their best under similar off-spec plate voltage conditions compared to the 6930's but what rolling I did do back when didn't sound bad either.

Cheers,
Morten

[tortugaranger]

Hi Hikmer.   Morten if your reading this.  Are you able to upgrade the LDR3000t with the new boards?

The short answer is yes but not quite yet. The LDR3000T is designed for a mix of single-ended and balanced audio so it needs a balanced LDR attenuator/controller. The V4 will handle balanced but not yet because the special V4 expansion board is not ready yet because simply haven't finished the work yet. It's next on the primary to-do list. The balanced version of the V4 does not use 2 V4 boards like the earlier V3s and V25s. The V4 system uses only 1 primary V4 board that handles single-ended and also the 2 phases of the right channel. A secondary V4 expansion board handles the 2 phases of the left channel. The primary V4 has a single microcontroller that handles everything while the expansion board has none is fully controlled by the primary board. I expect to finish out the design and testing of the V4 expansion board this month and have it ready in April.

[tortugaranger]

Here's the PCB layout for the V4 expansion board which is used together with primary V4 board for balanced audio applications. The expansion board has essentially the same layout and key control circuit as the primary board but is "headless" meaning it has no brain of its own. It's controlled entirely by the primary V4 board. In balanced audio applications the primary V4 board handles the right channel while the expansion board handles the left channel thus 4 total channels for balanced stereo attenuation.

The expansion board connects to the primary V4 board via a 14 pin ribbon cable. It's also 1 inch shorter but has the same width.

I'm waiting on blank boards from the fabricator which should be here in another week or so but what with all the tariffs and trade war noise there's a lot more uncertainty in shipment timing.

[tortugaranger]

Heh All,

I've been iterating on the design of the HPS.V4 Hybrid Power Supply and believe I'm all but done with the development work and am waiting on latest boards back from the fabricator. Meanwhile I took a few simple Input/Output readings to indicate overall performance. In this specific instance, the input to the HPS.V4 is from a typical 5 volt USB switching charger. Not the worst I've seen but not the best either. I'm showing the before/after (input/output) taken at both 1 ms (1000 Hz) and 100 us (10 kHz). Clearly there's more high frequency noise but this is to be expected with switching power supplies. This info was taken using a common LM1117 5 volt linear voltage regulator. Better performance is possible with a super-regulator such as the one made by Sparkos Labs.

The vertical units are in millivolts and the horizontal units are time.

Here's the AC component of the raw 5 volt input to the HPS.V4 at 1000 Hz. Not terrible - a few millivolts.






Here's the AC component of the 5 volt output from the HPS.V4 - at same 1000 Hz. Dead quiet at lower frequencies - well under a millivolt.




Next we take the same before/after look but with the sampling set higher at 100 us or 10,000 Hz.
Here's the raw 5 volt input. Clearly more noise at the higher frequencies but in absolute terms not awful at around +/- 10 millivolts.




Below, you see what the HPS.V4 does to the above waveform. Roughly a 10:1 reduction in noise magnitude.
Overall a very decent noise profile for a nominal 5 volt DC supply.